The present invention relates to a poppet valve for use in an internal combustion engine. Increased interest in improved fuel efficiency and increased power output of internal combustion engines has resulted in the internal combustion engines being operated at higher temperatures and at greater engine speeds. This places severe demands on all of the reciprocating components in the engine, including those in the valve train. In order to improve efficiency and fuel economy, the weight of all components that reciprocate is minimized.
In the case of the poppet valve components of the valve train, however, severe operating conditions place constraints on the materials that can be used to construct such valves. Poppet valves operate under severe conditions. The stem of the valve is subjected to cyclic loading at one end, sliding friction along its length and sometimes bending loads caused by misalignment of the valve head and the valve seat. The valve head is subjected to the most severe conditions, one side of which being exposed to the extremely high temperatures of combustion. In the case of the exhaust valve, the stem side face of the valve is subjected to the flow of hot combustion gases and, in addition, must provide an effective closure at the valve seat. Thus, there is repeated impact loading upon closure of the valve under the influence of the valve train.
In light of these conditions, interest has been expressed in forming such poppet valves from titanium alloys. An article entitled, "Titanium in Engine Valve Systems," by J. E. Allison et al., Journal of Metals, March 1987, pp. 15-18, fully discloses the reasoning behind the interest in titanium poppet valves for use in internal combustion engines.
In response to the demand for higher performance of valve train components, a number of different valve configurations have been proposed. U.S. Pat. No. 4,073,474 to Hashimoto et al. discloses a forged poppet valve where the head and part of the neck of the valve are made of a superalloy, while the stem is made of a conventional steel composition. Similarly, U.S. Pat. No. 3,300,303 to Leach discloses making a composite article from a wrought shaft with an end member formed from powder material affixed thereto. FIG. 2 of this reference depicts a poppet valve embodiment. A different approach is set out in U.S. Pat. No. 4,433,652 to Holtzberg et al., which discloses a multipart poppet valve having a stem of plastic material with the head of the valve formed of more heat resistant material, such as metal or ceramic.
All of such efforts are directed to form a lightweight, durable, heat-resistant poppet valve that can stand the environment and mechanical stresses imposed by its use in the valve train of a modern high performance internal combustion engine. Therefore, it is one object of the present invention to provide a titanium poppet valve having properties of the valve head and stem adapted to the physical environment of a high performance internal combustion engine.
It is another object of the present invention to provide a titanium poppet valve that can be readily manufactured by modern powder metallurgy techniques.
It is an additional object of the invention to provide a titanium poppet valve with a head portion of a different composition than the stem portion.
It is a further object of the invention to provide a titanium poppet valve formed of different titanium materials having a bond therebetween with no significant compositional gradient.
Other objects of the invention will be apparent from the description of the preferred embodiment or can be learned from practice of the invention.